We've been using this recipe to make laundry detergent. Works fine, but after a few days it disassociates into a clear bottom layer and a pink top layer. It's mildly annoying to have to re-stir it every time. Can we do something about it?
You should use about 0.25 - 0.35% xanthan gum (thickening agent) per the total weight of the mixture. Using xanthan gum is kind of tricky. You want to thoroughly mix the gum with the baking soda and washing soda (maybe in a bag), and slowly add the sodas to the water while mixing. If you don't do this, the xanthan gum will form lumps that are difficult to manage.
Hydroxyethyl cellulose might also work as a thickener, but it could increase the sudsing effect. Also, I would try adding a dash of dish soap; only use about 1% of the total weight of the mixture though, or else the sudsing effect will cause the washing machine to foam over.
It sounds like your emulsion is breaking down. Borax is used an emulsifier to get the soap molecules to mix more effectively in water (soap itself is an emulsifier, which is why it is able to remove grease and other hydrophobic molecules in water wash. In fact, most of the active ingredients in detergent are emulsifiers or surfactants of some sort). There are a number of factors that could be contributing to this, including the hardness of your water, and the actual ingredients you use.
There are a couple of things you could do to try to form a more permanent emulsion:
- increase the amount of borax in the recipe.
- make sure you dissolve your borax fully in warm water before it is mixed in.
- Mix well. By well, I mean get a paint mixer on the end of a power drill and have a cuppa while you mix it.
- As you are making an oil-in-water emulsion, you might consider combining (and dissolving) all ingredients EXCEPT the melted soap first, and then add the melted soap slowly as you mix well (see above for definition of mix well).
- try adding an additional emulsifier to assist stabilising the emulsion. You could cheat and add a little commercial liquid detergent as a starter.
The laundry soap recipe contains 3 classes of reagents: 1) Pure Soap (sodium stearate), 2) dispersant (borax adsorbs on clay and other solid particles, conferring a negative charge, and borax is also alkaline: pH~9.2) and 3) alkalizers (Na2CO3, pH~11.6) and sodium bicarbonate (pH~8.3).
The CRC Handbook lists sodium stearate as "soluble", but that needs qualification. A 2% solution is clear or nearly clear (but has a strong Tyndall effect); a 10% "solution" is quite turbid; and higher concentrations may separate quickly into layers. This separation is favored by a high ionic strength. NaCl is used commercially to "salt out" sodium stearate from the hydrolysis of tristearin (beef fat).
Thorough mixing of the warm sodium stearate mixture will help homogenize the mixture, but borax, sodium carbonate and sodium bicarbonate all tend to favor salting out the sodium stearate.
A cleaner can be optimized for the dirt it is supposed to remove. If your dirt is more oily/greasy, you may not need so much borax or sodium bicarbonate. Less salt will give a more stable solution. If your dirt is more clayey, dusty, or muddy, then less soap and more dispersant and alkalizers will work better (and the lower concentration of stearate would be stable longer).
Another possibility is to start with a soft soap (made from oleic acid). These tend to be less prone to separation because they form more viscous associations and are less solid when they begin to separate. The foaming could vary and be more significant for HE washing machines however.